Taizoon Canteenwala

INTRAMOLECULAR ELECTRON-TRANSFER OF C60-OLIGOANILINE LEUCOEMERALDINE CONJUGATES UPON PHOTOACTIVATION

ABSTRACT Conductive starburst C60-derived macromolecules were synthesized using C60(NO2)6 as a precursor intermediate for linking π-conjugate oligomers, such as tetraaniline and hexadecaaniline, directly onto the fullerene cage. Subsequent phenylhydrazine reduction of the resulting hexa(tetraanilino)[60]fullerene and hexa(hexadecaanilino)[60]fullerene emeraldines produced the corresponding leucoemeraldine donors. Photoexcitation of these hexa(oligoanilino)[60]fullerene leucoemeraldines under N2 induced intramolecular electron-transfer from benzenoid moieties of oligoaniline arms to the C60 cage, that regenerated the emeraldine structure in oligoaniline arms. Proceeding on the number of electrons transferred was followed and estimated by in situ chemical trapping method on the reaction of electrophiles with fullerenic anions generated. That substantiated the capability of the fullerene cage to accept multiple electrons during the irradiation process.

Comparison of the aggregation behavior of water-soluble hexa(sulfobutyl)fullerenes and polyhydroxylated fullerenes for their free-radical scavenging activity

We study the aggregation behavior of two highly water-soluble fullerene derivatives, hexa(sulfobutyl) fullerenes (FC4S) and polyhydroxylated fullerenes (fullerenols) [C60(OH)18] using small-angle x-ray scattering. We found that FC4S forms spheroidal aggregates having a similar radius of gyration Rg ≈ 19 A, in a wide concentration range from 0.4 to 26 mM in water solutions, whereas the mean sizes observed for C60(OH)18 aggregates in water solutions grow nearly two fold from R g = 20 A to R g = 40 A as the concentration increases from 0.7 to 50 mM. The implication of the structural differences between the two fullerene derivatives on their free-radical scavenging activity is discussed.

Synthesis and characterization of nitrated [60]fullerene derivatives

A synthetic method for the preparation of monodisperse hexanitro[60]fullerenes 16 was developed. The use of 16 as a reactive precursor in the synthesis of organo-amino derivatives of C60 was also demonstrated. The allylic tert-nitro moieties in hexanitro[60]fullerenes were found to be excellent leaving groups for nucleophilic substitutions by amino nucleophiles, such as anilines, leading to the formation of hexaanilino[60]fullerenes. Negative ion desorption chemical ionization mass spectra (DCI–-MS) of both hexaanilino[60]fullerene and hexanitroso[60]fullerene, a hydride-reduced product of 16, were utilized for substantiation of the number of nitro groups per C60 in 16. Detection of the molecular ion of C60(NO)6 at m/z 901 was correlated to the composition of its parent compound 16, as hexanitro[60]fullerenes containing 6 nitro addends per C60 cage.

Stable poly(fullerene oxide) thin films derived from hexanitro[60]fullerene

A new approach for the fabrication of poly(fullerene oxide) thin films that are stable up to 800 K and above by thermal treatment of hexanitro[60]fullerene is described. The reaction proceeds via the rearrangement of fullerenic nitro moieties and cleavage of the –O–NO bond in the nitrito groups; spectroscopic and mass spectrometric evidence for the oligomeric structure is presented.

SANS and SAXS study on aqueous mixtures of fullerene-based star ionomers and sodium dodecyl sulfate

Fullerene-based star ionomer C60[CO(CH2)5O(CH2)4SO3Na]6(FC10S), with six sodium-dodecyl-sulfate-like arms randomly bonded on the fullerene, has been synthesized. This novel molecule has a high water solubility and a structural shape resembling the skeleton of a micelle of sodium dodecyl sulfate (SDS). We study aqueous mixtures of the C60-based ionomers and SDS using small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS). With a selected deuteration of SDS, we have identified the formation of complex aggregates of FC10S with SDS in the mixtures. The structural information of the complex aggregates is extracted from the SANS and SAXS data measured for the mixtures. On the average, the complex aggregates observed have a cylinder-like shape with a radius of 19A and a length of ≈100A for the sample mixtures containing 2.3 or 1.2mM of FC10S and 6mM of SDS. The mean aggregation numbers of FC10S and SDS in each complex aggregate are 15 and 11, respectively.

Free Radical Scavenging and Photodynamic Functions of Micelle-like Hydrophilic Hexa(sulfobutyl)fullerene (FC4S)

Biological applications of water-soluble hexa(sulfobutyl)fullerene (FC 4 S) are reviewed. It was synthesized in a yield of 80–85% by the treatment of C 60 in dimethoxyethane (DME) with sodium naphthalide (10 equiv.) at 25 °C, followed by reacting the resulting hexa-anionic fullerene intermediates with an excess of 1,4-butane sultone (15 equiv.). FC 4 S showed an enhanced superoxide radical (O 2 −. ) scavenging activity and suppression efficiency against the superoxide-induced ferricytochrome c reduction under physiologic conditions, as compared with those of fullerenols at a dose level of 100 μ m. For example, a profound suppression efficiency of 60 and 96% was detected at a dose level of 50 and 100 μ m, respectively. Aggregation behaviors of FC 4 S molecules in aqueous solution were investigated using SAXS (small-angle X-ray scattering) and SANS (small-angle neutron scattering) techniques. We concluded that the aggregation size and shape of FC 4 S nanoparticles with the radius of gyration,R g of 18.9–19.1 A remain relatively unchanged with the variation of concentration in the concentration range of 0.35–26.0 mM. The phenomena were correlated to a high total surface area of nanoparticles and interfacial accessability of fullerene cages to reactive oxygen radical species.

RAPID SULFATION KINETICS OF FULLERENE IN OLEUM-OXIDE MIXTURES

Fast kinetics of fullerene sulfation reaction was observed in H2SO4–SO3 (28–30%) in the presence of metal oxides, such as V2O5 and, to a lesser extent, SeO2, showing nearly spontaneous production of hexacyclosulfated C60. Detection of dodecahydroxylated C60 in the reaction products revealed formation of hexacyclosulfated C60 even at an early stage of reaction. Partially sulfated C60 molecules exhibit a higher reactivity toward further sulfation than the parent fullerene molecules. A much faster sulfation rate of C60 in comparison with that of C70 under similar reaction conditions allows one to produce relatively pure dodecahydroxy[60]fullerene from a mixture of C60 and C70.

Synthesis of starburst hexa(oligoanilinated) C60 using hexanitro[60]fullerene as a precursor

Efficient syntheses of starburst hexaanilino, hexa(dianilino), hexa(tetraanilino), and hexa(hexadecaanilino)[60]fullerenes (HHDAF) were demonstrated using hexanitro[60]fullerene (HNF) as a reactive precursor molecule. The tertiary nitro groups of HNF were found to act as excellent leaving groups for replacement by a nucleophilic substituent. Utilizing this reactivity with electron-donor nucleophiles, a synthetic approach was developed for the production of oligoanilinated fullerenes as intramolecular donor–acceptor A–(D)6 starburst macromolecules with a well-defined arm number and chain length. The reactivity of HNF with oligomeric anilines increases with increasing number of repeating aniline units. Only an equal molar quantity of tetraaniline and hexadecaaniline was necessary for a complete reaction with HNF under mild conditions. The quantitative measurement of the material’s proton counts over the 1H NMR spectrum was utilized for determining the number of addends per C60 in the composition of oligoanilinated fullerenes. As a result, the NMR data fits well with the structure of tetraanilinated and hexadecaanilinated fullerenes, containing 6 tetraanilino and hexadecaanilino arms per C60, respectively. This composition of HHDAF was also supported by the DCI–-MS spectroscopic data showing an approximate correlation of the total relative peak intensities of fragmented oligoanilino mass ion groups. The optical properties of hexa(hexadecaanilino)[60]fullerenes revealed a close similarity with that of high molecular weight polyanilines.

Oxidation of C60-bound oligoaniline leucoemeraldine upon photoactivation

Phenylhydrazine reduction of hexa(tetraanilino)[60]fullerene and hexa(hexadecaanilino)[60]fullerene emeraldines produced the corresponding leucoemeraldines. Photoexcitation of hexa(oligoanilino)[60]fullerene leucoemeraldine under N 2 induces electron transfer from benzenoid moieties of arms to C 60 that regenerated the emeraldine structure in oligomers.